With regard to the processing of silver halide photographic light-sensitive materials, there has lately been growing a demand for shortening the processing period of time and reducing the discharge of waste processing solutions. In the medical field, for example, there have been sharply increasing medical examinations, including general diagnoses and treatments, attributed to the recently widespread regular medical checkups and complete physical examinations anyone can get hospitalized to undergo, and therefore the number of X-ray films to be radiographed and processed vastly increases, thus leading to a growing demand for the realization of techniques for super-rapidly processing radiographed films and for reducing the amount of waste processing solutions discharged at the time of the processing.
In order to speed up the processing, it is necessary to shorten each of the developing, fixing, washing and drying periods of time, but it results in the increase in the load in each processing step. For example, if the developing time is merely shortened, in the case of a conventional light-sensitive material, it causes the image density to lower, resulting from the sensitivity drop and the deterioration of image gradation. Where the fixing time is shortened, no complete fixation of the silver halide can be achieved to cause the resulting image quality to be degraded. Further, the processing time shortening makes the sensitizing dye's elution incomplete in each of the developing, fixing and washing steps to thus cause the resulting image to be degraded with a residual dye stain. Accordingly, the solution to the above problems requires the speedup of the developing and fixing rates, the reduction in the amount of sensitizing dyes, and the acceleration of the elution and/or decoloration of the sensitizing dye.
On the other hand, the reduction in the discharge amount of waste processing solutions needs to make each processing solution less exhaustible and/or less replenishable, but is accompanied with the same problems as in the above speedup case.
To solve the above problems, EPO506,584, Japanese Patent Publication Open to Public Inspection (hereinafter abbreviated to JP O.P.I.) Nos. 88293/1993 and 93975/1993 disclose techniques which use benzimidazolocarboxycyanines well decolorable as spectral-sensitizing dyes. Also, JP O.P.I. No. 61148/1993 discloses techniques in which oxacarbocyanines and benzimidazolocarboxycyanines as spectral-sensitizing dyes are combinedly used in a specific proportion to a silver halide emulsion having an iodide content of not more than 1 mol %, and the emulsion is further chemically sensitized with a selenium compound and/or a tellurium compound.
However, the use of these disclosed techniques alone, although effective in the residual dye stain improvement, is still not sufficient to satisfy the recent demand levels to various photographic characteristics, particularly to increasing the sensitivity. Further, the above techniques have the disadvantage that the light-sensitive material, when stored in an atmosphere at a high humidity and a high temperature, shows a significant sensitivity drop.
Incidentally, there have recently been disclosed many higher-speed/higher-quality-image-achieving techniques to use tabular silver halide grains, which are described in JP O.P.I. Nos. 111935/1983, 111936/1983, 111937/1983, 113927/1983 and 99433/1984. Further, JP O.P.I. No. 92942/1988 discloses a technique to provide a high silver iodide content core inside the tabular silver halide grain, and JP O.P.I. No. 151618/1988 discloses a technique to use hexagonal tabular silver halide grains for obtaining an increased sensitivity.
In addition to the above, JP O.P.I. Nos. 106746/1988, 183644/1989 and 279237/1989 disclose techniques pertaining to the composition distributions of tabular silver halide grains.
In regard to the crystal structure of the tabular silver halide grain, some techniques about the configuration of grains and parallel twin planes are disclosed; for example, JP O.P.I. No. 131541/1989 discloses a technique to use circular tabular grains for improving the photographic speed and graininess.
JP O.P.I. No. 163451/1988 discloses a technique to use a tabular silver halide grain having parallel two or more twin planes in which the (b/a) ratio of (b) to (a) equals to 5 or more, wherein (a) represents the distance between the twin planes in the tabular silver halide grain and (b) represents the thickness of the grain, said technique being effective in improving both sensitivity and graininess. The publication describes a technique to raise the inter-grain uniformity of the distance between the twin planes to thereby increase the sensitivity and improve the graininess.
WO91/18320 discloses a technique to use a tabular silver halide grain in which the distance between its twin planes is less than 0.012 .mu.m, and describes that it enables to accomplish a high sensitivity.
EP515894A1 describes that raising the sensitivity can be attained by making less than 75% the (111) face proportion to the edge plane of a tabular silver halide grain of which the tabular property defined by (grain diameter )/(grain thickness ).sup.2 is 25 or above.
On the other hand, there are also disclosed many techniques for improving tabular silver halide grains by removing their shortcomings therefrom. JP O.P.I. No. 142439/1991 discloses a technique to improve the storage stability in a moist ambience of an emulsion of silver halide grains comprising tabular grains each having an aspect ratio of 3 or more and also having (111) and (100) faces.
The tabular silver halide grain, since its surface area is larger in the same volume than those of silver halide regular crystal grains such as hexahedral and octahedral grains, makes it possible to increase the adsorption amount of a sensitizing dye to its grain surface, and therefore is considered to have the advantage that it is easy to increase its sensitivity and improve its sharpness due to reduction in scattering light.
In fact, however, even when a sensitizing dye in an increased amount in proportion to the surface area of the tabular grain is used, the sensitivity of the grain can not become as much high as expected, and in addition, as the shortcomings of the tabular grain the color stain due to the residual dye and the image quality degradation have now been actualized as the problems in speeding up the processing.
In the case where various water-insoluble photographic additives are introduced into a silver halide emulsion, a method of adding to the silver halide emulsion a solution of such photographic additives dissolved in an organic solvent such as methanol is prevailing. Instead of such the conventional method, an attempt also is made to disperse photographic additives in the presence of a wetting agent and a dispersant without using any organic solvent to prepare an aqueous solution thereof, and the obtained aqueous additives dispersion is added to the silver halide emulsion. Namely, JP O.P.I. No. 110012/1977 describes a method in which a sensitizer is pulverized in the presence of a dispersant (surfactant) providing a certain surface tension in an aqueous phase, and the obtained aqueous dispersion is dehydrated to be dried, and then the product, either as it is or after being dispersed in an aqueous gelatin solution, is added to the silver halide emulsion.
JP O.P.I. No. 102733/1978 describes that a uniform mixture (pasty mixture) of a photographic particulate additive, a dispersant such as sorbitol and a protective colloid such as gelatin is prepared to be made in the noodle form and then dried in a hot air to thereby provide a granulated product, which is then added to a photographic aqueous colloidal composition for coating.
U.S. Pat. No. 4,006,025 describes a method in which a spectral-sensitizing dye is mixed with water to be made in the slurry form, and then uniformly dispersed at a temperature raised to 40.degree.-50.degree. C. in the presence of a surfactant into water, and the dispersion is added to the silver halide emulsion.
These methods are ones for adding photographic additives such as spectral-sensitizing dyes in an aqueous phase without using any organic solvents. However, they have the following problems in practical use. That is, since the aqueous dispersion is pulverized according to a freeze-drying process, and the time required for the adsorption of additives such as spectral sensitizers onto the silver halide grain is prolonged, so that a desired photographic sensitivity can not be obtained within a short spectral and chemical sensitizations period of time, and such the silver halide emulsion, when coated, produces precipitates that tend to cause a coating defect. In addition, the use of a wetting agent or a dispersant for dispersing the additives is liable to destruct the emulsified substance present in the silver halide emulsion; to increase coating troubles in the high-speed coating of the silver halide emulsion or to bring about quality problems such as the poor adhesion trouble of the resulting silver halide photographic light-sensitive material product.